Effect of Back Support Condition on Seat to Head Transmissibilities of Seated Occupants under Vertical Vibration

Abstract

The seat-to-head transmissibility (STHT) of seated human subjects has been investigated through measurements of vertical seat vibration transmitted to the head in both vertical and fore-and-aft directions. The experiment was performed using 12 adult male subjects exposed to whole-body vertical random vibration in the 0.5–15 Hz frequency range. The effects of back support conditions on the transmitted vibration were investigated by considering three back support conditions (No back support, vertical back support, and inclined back support), and two different hands positions (hands in lap and hands on the steering wheel) while exposed to three magnitudes of excitation (0.25, 0.5 and 1.0 m/s2 rms acceleration). A helmet-strap-mounted accelerometer mounting system was designed to measure the head acceleration motions along the three translational axes. The results attained from ANOVA suggested a strong influence of the back support condition on the magnitude of both the vertical and fore-and-aft STHT. The results also revealed the nonlinear response of the seated body with respect to the excitation magnitude, while the effect of hands position was judged to be insignificant.